no. 3
Floquet operators with singular spectrum. II
Annales de l'I.H.P. Physique théorique, Tome 50 (1989) no. 3, pp. 325-334. 
@article{AIHPA_1989__50_3_325_0,
     author = {Howland, James S.},
     title = {Floquet operators with singular spectrum. {II}},
     journal = {Annales de l'I.H.P. Physique th\'eorique},
     pages = {325--334},
     publisher = {Gauthier-Villars},
     volume = {50},
     number = {3},
     year = {1989},
     zbl = {0689.34023},
     mrnumber = {1017967},
     language = {en},
     url = {http://archive.numdam.org/item/AIHPA_1989__50_3_325_0/}
}
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Howland, James S. Floquet operators with singular spectrum. II. Annales de l'I.H.P. Physique théorique, Tome 50 (1989) no. 3, pp. 325-334. http://archive.numdam.org/item/AIHPA_1989__50_3_325_0/

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